1. Field of the Invention
The present invention relates to a recovery type steam cooled gas turbine, and more particularly to a recovery type steam cooled gas turbine for warming steam cooling passages of combustor walls, moving blades, stationary blades, a rotor or the like upon starting the gas turbine, for preventing dew formation when feeding the steam, and for preventing rust generated by the condensed steam during the stopping operation.
2. Description of the Related Art
Recently, the combustion temperature of combustion gas for gas turbine has been increasing in accordance with demands for higher efficiency in power generation plants. Consequently, high temperature exhaust gas from a gas turbine is introduced into a waste heat recovery boiler and the exhaust gas heats the boiler to generate steam. Moreover, a composite power generation plant driven by a steam turbine using this steam has been developed. In such a composite power generation plant, a steam cooling method with superior cooling performance has been proposed for cooling high temperature components of the gas turbine instead of using an air cooling method.
FIG. 8 shows one example of the above-described steam cooled type gas turbine, and in particular shows an operation method when starting. In FIG. 8, numeral 70 denotes the gas turbine, numerals 71-1, 71-2 and 71-3 denote stationary blades, numerals 72-1, 72-2 and 72-3 denote moving blades, and numeral 73 denotes a rotor of the gas turbine 70. Numerals 74, 75, 76 and 77 denote three-way valves, respectively. Numeral 80 denotes a steam feed pipe. Numeral 81 denotes an air feed pipe for introducing cooling air from a compressor (not shown) to the turbine blades. Numeral 82 denotes an air return pipe. Numerals 83 and 84 denote pipes for feeding the air or the steam cooling medium to the stationary blades 71-1 to 71-3, respectively, and recovering it (In FIG. 8, this is only shown for the stationary blade 71-1 and the others are omitted). Numerals 85 and 86 denote pipes for feeding the cooling medium to the moving blades 72-1 to 72-3, respectively, and recovering it. In the same manner, this is only shown for the moving blade 72-1 and the others are omitted. Numeral 87 denotes a pipe for connecting the three-way valves 77 and 75 to each other.
In the starting operation of thus constructed gas turbine, the three-way valve 77 is switched to close the steam feed pipe 80 side and open the air feed pipe 81 side to introduce the air from the compressor through the pipe 81 to the pipe 87. This air is used as the cooling air for cooling the turbine blades during regular operation, but is used for warming the passages within the turbine blades during the starting operation. Thereafter, the air passes through the pipe 83 via the three-way valve 75 and is introduced to and passed the stationary blades 71-1 to 71-3. Then, the air which has been passed out of the stationary blades passes through the pipe 84 and the three-way valve 74 and is recovered on the compressor side from the three-way valve 76 through the pipe 82. Also, at the same time, the air passes through the pipe 85 from the three-way valve 75 and is introduced into the moving blades 72-1 to 72-3 to be passed through the moving blades. The air that has been passed out of the moving blades passes through the pipe 86 and the three-way valve 74, to be recovered on the compressor side from the three-way valve 76 through the pipe 82.
When the stationary blades 71-1 to 71-3 and the moving blades 72-1 to 72-3 are warmed by the air from the compressor to a temperature that is suitable for the steam flow, the three-way valves 77 and 76 are switched to close the air feed pipes 81 and 82 and open the steam feed pipe 80 to feed steam to the gas turbine blades instead of the air from the compressor. Then, when the steam passes through the stationary blades 71-1 to 71-3 and the moving blades 72-1 to 72-3, the gas turbine enters normal operating conditions.
Thus, in the starting operation of the gas turbine, the cooling air from the compressor to be used as the cooling medium for cooling the high temperature components during regular operation is used for warming the flow passages within the gas turbine blades. When the temperature of the flow passages, i.e., the cooling medium flow passages, becomes, due to the air from the compressor, equal to or higher than a temperature at which dew is not formed when the steam flows, the three-way valve is switched to stop the flow of the cooling air and circulate the cooling steam.
Subsequently, FIG. 7 shows another example of a method for starting a gas turbine using a steam cooled system. In FIG. 7, a gas turbine system 101 is composed of a compressor 104, a combustor 106 coupled with the compressor 104 and a gas turbine 108 rotatably driven by the combustion gas. The compressor 104 and the gas turbine 108 are connected to each other through a single axis and are connected to the power generator 100a. 
A steam turbine system 102 is composed of a waste heat recovery boiler 112 for introducing the waste gas from the gas turbine 108 through an exhaust gas passage 111, a steam turbine 114 rotatably driven by the steam fed from the boiler 112 through a steam passage 113b and a steam condenser 116 for converting back into water the waste steam (gas-liquid two-phase flow) of the steam turbine 114 introduced through a waste steam passage 115. The condensed water generated in the steam condenser 116 is circulated to the waste heat recovery boiler 112 through a condenser pump 117 and a condenser pipe 118. A power generator 100b is connected to the steam turbine 114. Regulator valves 119a and 119b and check valves 200a and 200b are provided in the steam passages 113a and 113b, respectively. Also, a regulator valve 121 is provided in the steam passage 115.
A cooling steam system 103 for cooling the gas turbine 108 is composed of a main system 122a and an auxiliary system 122b. The main system 122a is detoured so as to introduce a portion of one steam passage 113a to the stationary blades or moving blades which are the high temperature area 123 of the gas turbine 108 of a gas turbine system 101. The steam feed source is the waste heat recovery boiler 112.
In the auxiliary system 122b, the steam generating portion is connected to one steam passage 113a of the main system 122a by an auxiliary steam passage 127 having a check valve 125 and a regulator valve 126, so that the auxiliary steam is fed to the high temperature area 123 of the gas turbine 108. After cooling the high temperature area 123, the auxiliary steam is fed to the steam turbine 114 and discharged to the waste steam passage 115. An auxiliary circulation passage 128 is connected to the waste steam passage 115 so that the waste steam is circulated to the auxiliary boiler 124 through the auxiliary circulation passage 128. A regulator valve 129, a steam condenser 130 and an auxiliary steam pump 131 are provided along the flow direction at the auxiliary circulation passage 128.
The gas turbine 108 is started only when the auxiliary boiler 124 has already started. In the initial stage, the regulator valve 126 of the auxiliary steam passage 127 is opened, and the cooling auxiliary steam is fed from the auxiliary boiler 124 through the check valve 125 to the high temperature area 123 within the gas turbine 108. The cooled steam is introduced to the steam condenser 130 through the steam turbine 114 and the regulator valve 129 of the auxiliary circulation passage 128 and is returned as water back to the auxiliary boiler 124 by the auxiliary steam condenser pump 131.
The amount of steam generated from the waste heat recovery boiler 112 is small in the initial stage of the starting operation. Accordingly, the regulator valve 119a of one steam passage 113a is closed, and the steam is not used for cooling. The regulator valve 119b of the other steam passage 113b is opened so that the steam is fed to the steam turbine 114 which can sufficiently use such an amount of steam. On the other hand, after passage of a certain period of time during which the amount of steam generated by the waste heat recovery boiler 112 of the main system 122a is increased so that enough steam may be obtained, the regulator valve 119a of the one steam passage 113a is opened and the steam of the waste heat recovery boiler 112 is fed to the gas turbine 108 side to be used as the cooling steam. The auxiliary boiler 124 is stopped after the predetermined amount of steam can be obtained from the waste heat recovery boiler, after passage of a certain period of time from the starting.
During operation thereafter, the high temperature exhaust gas of the gas turbine 108 is fed to the waste heat recovery boiler 112 to generate steam through heat exchange with water. A portion of the generated steam passes through the regulator valve 119a and is used as the cooling steam for cooling the gas turbine stationary blades, and then is fed to the steam turbine 114. On the other hand, another portion of the steam is fed directly to the steam turbine 114 through the regulator valve 119b and expands to generate power. The steam water discharged from the steam turbine 114 is converted into water in the steam condenser 116 and is circulated to the waste heat recovery boiler 112 by the steam condenser pump 117. The gas turbine 104 and the steam turbine 114 drive the power generators 100a and 100b, respectively.
There are two types of operating methods for starting the above-described conventional gas turbine using a steam cooling system. In one operating method, after the air made to flow to the gas turbine high temperature area from the compressor during starting and the high temperature area reaches a suitable temperature for the steam to flow, the valve is switched to allow the steam to flow for regular operation. In the other operating method, during starting, the steam is made to flow from the auxiliary boiler to the high temperature area to initialize the operation, and thereafter the steam from the waste heat recovery boiler is used for regular operation.
Since it is impossible to obtain cooling steam at a suitable temperature in the starting operation of the gas turbine because the waste heat from the gas turbine has a low temperature and the heat capacity of the pipes of the waste heat recovery boiler is limited, there has been a problem in that dew condenses in the steam cooling passages in the gas turbine blades. Consequently, as described above, it has been necessary to use the steam from the auxiliary boiler or air from the compressor when starting the gas turbine so that the steam cooling passages warm up. It has also been necessary to protect the respective steam cooled portions from the combustion gas generated in the gas turbine so that high temperature gas is prevented from entering the steam cooled portions.
The above-described conventional methods attain these objects, but it is necessary to use large scale equipment such as an auxiliary boiler.
Accordingly, in order to attain the above-noted objects, a recovery type steam cooled gas turbine is provided having equipment that warms up steam cooled portions in a starting operation without using large scale components such as an auxiliary boiler, prevents for draining when feeding the cooling steam, securely prevents penetration of high temperature combustion gas, eliminates the residual steam even during stoppages, and prevents rust caused by condensation of the residual steam.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a recovery type steam cooled gas turbine comprising: a system for recovering waste heat of the gas turbine by means of a waste heat recovery boiler and for driving a steam turbine; and a steam system in which at least a wall surface of a gas turbine combustor, steam cooling passage systems of some moving blades of the gas turbine, steam cooling passage systems of some stationary blades of the gas turbine, a steam cooling passage system of a gas turbine rotor and/or a system combining them is cooled with steam generated in the waste heat recovery boiler and/or steam having suitable pressure and temperature taken from steam that has passed through the steam turbine, and is thereafter recovered to at least one of the waste heat recovery boiler, the steam turbine and a steam condenser, characterized in that said gas turbine further comprises a medium feed system for causing, in a starting operation and/or a stopping operation of the gas turbine, a predetermined medium to flow through said steam cooling passage system and said system combining them while being isolated from the other systems.
When starting a gas turbine, since the waste heat of the gas turbine is still low and also the heat capacity of the waste heat recovery boiler passages is large, it is impossible to obtain a suitable temperature steam even if the steam is made to pass therethrough. Consequently, dew condenses in the steam cooling passages or the high temperature combustion gas is introduced into the steam cooling passage during the starting operation. Accordingly, with a gas turbine according to a general aspect of the present invention, the steam cooling passage system is isolated from the other systems and is connected to the medium feed system using a medium other than steam, air for example, to perform a warming-up operation. This warming-up operation is performed so that the temperature of the steam cooling passages is made to be close to the steam temperature. Then, the valves are switched to connect the steam cooling passage to the steam system to make the steam flow for normal operation.
Thus, such a warming-up operation of the gas turbine is performed when starting the gas turbine to thereby prevent dew from condensing in the steam cooling passages when feeding the steam and prevent an unbalance or vibration of the rotor due to the dew condensation. Also, during the warming-up operation, since the medium is made to flow through the steam cooling passages, it is possible to prevent the high temperature combustion gas from penetrating thereinto.
In a preferred mode for carrying out the invention, when starting the gas turbine, said steam cooling passage system is kept at a pressure higher than that of the combustion gas that passes through an interior of the gas turbine so as to prevent the combustion gas from leaking into the passage system.
In another preferred mode for carrying out the invention, the medium that flows through said steam cooling passage system is steam that is kept at a pressure higher than that of the combustion gas.
Since the pressure of the medium that passes through said steam cooling system is higher than the pressure of the outside combustion gas, it is possible to positively prevent the high temperature gas from penetrating into the steam cooling passage system when starting the gas turbine, and the oxidation and the like of the interior of the passages by such gas can be prevented.
In yet another preferred mode for carrying out the present invention, a compressor and a temperature adjuster for the predetermined medium are provided in said medium feed system.
Since the compressor and the temperature adjuster are provided in the medium feed system, the medium is pressurized thereby making it easy to circulate the medium. Also, a suitable temperature adjustment can always be performed so that the temperature of the medium is suitable for the warming-up operation.
In still another preferred mode for carrying out the invention, said medium feed system changes the temperature of the predetermined medium between an initial stage and a later stage of the starting operation of the gas turbine, and the temperature of the predetermined medium in the later stage is higher than the temperature of the predetermined medium in the initial stage.
In the initial stage of the starting operation, since the moving blades of the gas turbine are at a low temperature in the range of from room temperature to about 300xc2x0 C., the warming-up operation is performed so that the temperature of the medium matches this temperature. In the later stage of the starting operation, the temperature of the gas turbine moving blades is high, in the range of about 300 to 500xc2x0 C. Accordingly, the temperature of the medium is also increased to match this change. As a result, since the warming-up operation is performed while keeping the temperature of the medium in conformity with the temperature elevation of the moving blades, the temperature difference between the moving blades and the medium is eliminated, and there is not only no dew condensation in the starting operation, but also none during the feeding of the steam so it is possible to positively prevent vibrations or unbalanced rotation due to the dew condensation.
In still another preferred mode for carrying out the invention, the medium is air extracted from the compressor or an outlet air thereof.
Since the air is extracted from the compressor as the medium, the system for the medium may be simplified, and the adjustment of the temperature and the pressure may be readily performed.
In still another preferred mode for carrying out the invention, the medium is inert gas.
Since an inert gas other than that outside of the gas turbine system may be used as the medium, the range of the medium available for the warming-up operation in the starting operation of the gas turbine may be expanded.
In still another preferred mode for carrying out the invention, said medium feed system makes dry air to flow through said steam cooling passages during the stopping operation of the gas turbine and purges residual steam within said steam cooling passages to make it possible to discharge the residual steam to the outside.
In the stopping operation of the gas turbine, the steam remains in the steam cooling passages, and this residual steam condenses to generate rust or the like. However, by virtue of the structure described above, the dry air is passed through the steam cooling passages in the stopping operation and the residual steam is purged. Accordingly, it is possible to positively prevent the generation of the drain caused by the residual steam at all the times after the stopping operation.
According to an another aspect of the present invention, a recovery type steam cooled gas turbine in which a steam turbine is driven by the waste heat of the gas turbine, a portion of the steam is extracted from a steam system of the steam turbine and is introduced into and used to cool steam cooling passages kept at a high temperature in the gas turbine, and the steam after cooling is returned to and recovered by the steam system of the steam turbine, characterized in that said gas turbine further comprises a medium feed system for feeding a medium other than steam to said steam cooling passages by connecting inlet and outlet sides of the steam cooling passages in a starting operation and/or a stopping operation of the gas turbine.
The medium feed system that may be switched by the valves or the like is connected to the inlet and outlet sides of the cooling steam system to cause the medium other than steam, for example, air to flow for-the warming-up operation. This warming-up operation is performed so that the temperature of the steam cooling passages is made to be close to the steam temperature. Thereafter, the valves are switched to connect the steam cooling passage to the steam system to make the steam flow for regular operation.
Thus, such warming-up operation of the gas turbine is performed in the starting operation the gas turbine to prevent dew from condensing in the steam cooling passages when feeding the steam and to prevent unbalances or vibrations in the rotor due to the dew condensation. Also, during the warming-up operation, since the medium flows through the steam cooling passages, it is possible to prevent high temperature combustion gas from penetrating thereinto.